On 12/24/10, Michael Haufe (TNO) <t...@thenewobjective.com> wrote:
> On Dec 24, 6:43 pm, Garrett Smith <dhtmlkitc...@gmail.com> wrote:
>> The client of the API gets an interface object that has properties and
>> methods so instanceof and constructor shouldn't matter.
>
> instanceof is important for an interface consumer to be certain that
> they are using the proper object:
>
I disagree.
> function draw(group){
> if(group instanceof Group){
If the program is written so that group then it won't matter. The
program can be safe enough to not have to worry about that. Example:
var group = createGroup();
draw(group);
The program would be clear what `group can do at that point. The
constructor or prototype wouldn't matter; what matters at that point
is what `group` can do.
But if you're not sure at any point, then sure, you can use
inferential tests like this:
> if(typeof group == "object" && typeof group.method1 == "function"
> && typeof group.method2 == "function"
> && typeof group.method3 == "function"){
> //well, it looks like a group....
I don't like to see all that into an inline block. It is much less
cluttered if the typechecking is moved into a separate function, such
as:
if(Group.isGroupLike(group)) {
> group.method1();
> group.method2();
> group.method3(); //oops, its not the droid you're looking for
> } else {
> throw new Error("Shape Group Expected");
> }
> }
>
Better yet just get rid of the typechecking there.
But, when I want to use instanceof, which is rarely, it is inside scope.
For example, in domunit, there is a catch block that catches what
might be any of: A thrown custom error (EarlyExit or Wait), or a
runtime test error. EarlyExit and Wait are in the same scope so they
can't be coming from another frame and instanceof can work there.
--
Garrett
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